1. Field of the Invention
The present invention relates to an optical disc recording method and apparatus for recording information by forming a recording mark on a recording medium whose physical properties are different from those of the other portions of the medium.
2. Description of Related Art
Optical disc media such as DVD-RAM and DVD-RW that employ rewritable phase-change optical recording material are in widespread use. Recently, greater capacity Blu-ray Disc products that employ blue laser and that accommodate high-vision broadcast recording have also been put on the market. There is now a growing need for optical disc apparatuses capable of reading and writing DVDs and Blu-ray Discs on a single drive unit. When information is recorded on such high-density optical discs, it is important to optimize the power and pulse condition of the write laser beam in a process generally referred to as a test write.
Generally, for the quality evaluation of the signal recorded on an optical disc, jitter, which indicates the standard deviation of the displacement between data edge and clock edge, is used. In order to measure the jitter value, a dedicated measuring instrument such as a jitter analyzer is required. Since it is impossible to build a jitter analyzer, which is expensive, in the optical disc apparatus, there is a need for an alternative signal evaluation index.
In an example of the conventional test write technique, JP Patent Publication (Kokai) No. 10-320777 (corresponding to U.S. Pat. No. 6,269,062) discloses that, instead of directly measuring the jitter value, a logic pulse referred to as an error pulse is produced when the phase difference between data edge and clock edge exceeds a predetermined value, and the number of such error pulses is counted so as to evaluate the jitter value in an equivalent manner. The write power is then optimized based on the evaluation.
In WO01/011614 (corresponding to U.S. Pat. No. 6,654,325), a test write technique for the 4.7 GB DVD-RAM is disclosed which is based on a table-referenced type adaptive write strategy in accordance with the preceding and following space and mark lengths. In this technique, a sorting process is carried out on error pulses in accordance with a write strategy table, and the pulse condition of the write laser light is optimized such that the error pulse value of each table item is minimized. Although the actual sorting process requires two 4×4 tables, since a logic pulse called error pulse is used for signal evaluation, the sorting process can be easily implemented by means of a logic LSI.
Further, JP Patent Publication (Kokai) No. 2003-6864 A discloses a write condition optimizing technique suitable for binarization by the Viterbi decoding. In this technique, which is an evolution of the aforementioned method based on binarization by the conventional direct slice scheme, the read signal is A/D converted and then sorted depending on the temporal transition of the target signal level for the Viterbi decoding. The phase difference between the clock and the data edge is detected for each case of the read signal, so that an optimum write condition for the aforementioned Viterbi decoding scheme can be obtained.
Patent Document 1: JP Patent Publication (Kokai) No. 10-320777 A (1998)
Patent Document 2: WO01/011614
Patent Document 3: JP Patent Publication (Kokai) No. 2003-6864 A